Guidewires are frequently used in medical procedures to direct medical implements to specific locations within a patient's body. Most commonly, guidewires are used to define a path to a desired location within a patient's vascular system and a second device, such as a catheter, tracks along the guidewire until it reaches the desired location. Frequently, the desired location for the medical device can be rather distant from the point of insertion of the guidewire into a patient's vascular system; distances of up to 175 cm are not uncommon.
In standard practice, a guidewire will be introduced into a patient's vascular system at a location remote of the site to be accessed and guided through the vascular system. This is normally accomplished by using a remotely steerable guidewire which permits the operator to select a specific path through a maze of branching passages until the desired location is reached. This process of guiding the guidewire can take a fairly long period of time for certain operations, such as accessing selective sites within coronary vessels.
Once a guidewire is in the patient's vascular system, a catheter or other similar device will often be placed over the guidewire and urged along the guidewire through the vascular system. In some procedures, the catheter is passed over the guidewire shortly after the guidewire is introduced, leaving only the steerable tip of the guidewire to extend beyond the end of the catheter, and the catheter and guidewire are advanced together. In other instances, only after the guidewire is guided to a desired location is the catheter placed over the guidewire, and the catheter is then urged along the guidewire until it reaches its destination.
In some instances, though, it may be necessary to remove the first catheter from the patient's body and replace it with a different catheter or some other intravascular medical device. For instance, in balloon catheterization procedures for enlarging stenosed lengths of vascular channels, a first balloon catheter having a relatively small balloon may be used first. Then the first catheter may be replaced with a series of catheters having successively larger balloons or differently shaped balloons to further enlarge the channel.
Ordinarily, guidewires are generally only a little longer than the catheters with which they are used. If one were to remove the catheter, there would be no way to grasp the guidewire to hold it in place during this removal because it would be completely enclosed within the catheter's lumen. Obviously, it would be preferable to keep the guidewire in position so that it will not have to be guided once again to its desired location. In the past, the guidewire was commonly replaced with a much longer wire before removing the catheter. This "exchange wire" was commonly about twice the length of the guidewire it replaced (e.g. about 260 cm or longer), permitting an operator to maintain a grasp on the wire as the catheter was removed. The catheter would then be removed from the exchange wire and the exchange wire would be used to guide the next catheter to the desired location.
Such exchange wires solved the basic problem of maintaining guidewire position during catheter exchanges, but they presented additional difficulties of their own. For instance, if a particularly selective guidewire position was needed, sometimes the precise desired position would be lost during the exchange of the initial guidewire--when replacing the guidewire, it had to be removed prior to introducing the exchange wire. Removing the guidewire for exchange could cause the operator to lose a precise position of the distal end of the guidewire.
In order to solve this problem, means for adding an extension to the proximal end of the initial guidewire have been developed. In general, such guidewire extensions involve affixing a second guide wire, which may be referred to as an extension wire, directly to the proximal end of the initial guidewire without requiring the initial wire to be moved. This helps overcome some of the difficulties of the prior art in that it allows the operator to leave the original guidewire in place yet maintain a grip on either the guidewire or the extension wire as the catheter is removed.
However, this solution also presents some difficulties of its own, such as making a secure connection between the guidewire and the extension wire when both of these wires tend to have rather small diameters so they can fit in the lumen of a vascular catheter. The extension wire must be carefully formed to mate with the end of the original guidewire, increasing the costs of each of these components. This solution also requires that the original guidewire be of a type designed to be used in a catheter exchange procedure and increases the equipment costs for the procedure as the guidewire and extension wires are generally intended to be disposed after a single use. Furthermore, the extended guidewire tends to be extremely long, e.g. on the order of 3 meters, and can be relatively cumbersome to handle effectively.
Others have proposed alternative solutions. For instance, an international patent application published under the Patent Cooperation Treaty in the name of Baxter International Inc. (International Publication Number WO 93/05814), teaches a catheter having two lumens, one of which is adapted to receive a guidewire. This small "sublumen" within the overall catheter lumen is provided with a fracture line which allows the catheter to be split lengthwise to expose the guidewire. By splitting open the catheter along this seam one can take the catheter off of the guidewire without necessitating the removal of the guidewire from a position in the patient's body.
However, the solution proposed by Baxter has a number of drawbacks of its own. For example, the catheter used by Baxter must be used initially by the person performing the procedure. In some instances, the need for a different catheter is not realized until the operator has a first catheter in place and realizes it will not perform adequately. Accordingly, if a catheter such as that taught by Baxter is not used initially, one must still face the difficulties noted above in exchanging a standard catheter.